Flotation of calcium carbonate ores



Patented Sept. 9,1941

UNITED STATES. PATENT OFFICE FLOTATION OF CALCIUM CARBONATE ORES MikaelVogel-Jorgensen, Copenhagen, Denmark,

assignor, by. mesne assignments, to Separation Process Company, Boroughof Catasauqua, Lehigh County, Pa.', a corporation of Delaware NoDrawing. Application July 2, 1940, Serial No.

13 Claims.

This invention relates to the separation by froth flotation of calciumcarbonate minerals from pulps Containing them and is especiallyconcerned with rendering calcium carbonate ores more suitable for use inthe manufacture of cement, lime and like materials.

In floating calciumcarbonate particles from pulps containing suchparticles one or more flotation agents are added to the pulp to collectthe calcium carbonate in the froth. In some cases collecting agents(preferably emulsified or saponifled fatty acids) and frothing agentsare added separately, while in other cases a single substance will actboth as collecting and frothing agent, as is the case with saponifledtall oil. In actual fact this agent, the use of which in flotation isdescribed in my prior-U. S. Patent No. 2,165,268, contains both fattyacid soaps which act as collectors and resinacid soaps which act asfrothers. Now while in the flotation the calcium carbonate minerals .arefor the most part removed from the siliceous and other-impurities, aperfect separation of the calcium carbonate from the other substances isvirtually impossible, and a certain quantity of the siliceous mineralsappears in the concentrate .and a certain quantity of calcium carbonatein the reject. A concentrate containing a high calcium carbonate contentis referred to as a clean concentrate, and the higher the calciumcarbonate content the cleaner is said to be the concentrate.

It has now been found that better results, especially as regards thecleanness of the concentrate, are obtained when using resinate frothingagents if an adequate quantity of a mineral acid (e. g. sulphuric acid,hydrochloric acid, nitric acid or phosphoric acid) or of a soluble saltof an alkaline earth metal which forms. a resinate of relatively lowsolubility is incorporated in the pulp, and if the pulp on flotation hasa pH value of from 6 to 9, and preferably below 8. It appears probablethat the mineral acid or metal salt reacts in the pulp and causessomedegree of. precipitation of the resinate frothing agent,

either as resin acid or as the resinate of the metal present in themetal. salt, and thereby modifies the frothing action. By suchprecipitation the concentration of the resinate dissolved in the pulp isdecreased, regardless oi whether it is the insoluble hydrogen resinateor resin acid, or an alkaline earth metal resinate salt which isprecipitated. Furthermore, the mineral acids and the metal salts in manycases increase the selectivity of the fatty acid soap and similarcollecting agents used in floating calcium car- In Great Britain July 3,1939 a calcium salt, but salts of other metals, e. g. of

barium and magnesium, may be used. The salts whichare appropriate foruse in the process of my invention I have referred to herein and in theclaims as the alkaline earth metal salts and it is to be understood thatin using this designation I intend to include within its scope salts ofmagnesium. Where it is stated above that the metal salt is soluble," itis meant not that the saltis necessarily highly soluble, but that it issufiiciently soluble in the pulp to give the desired effect on theflotation. That is, the solubility should be in excess of that of thecorresponding resinate salt. Thus calcium sulphate, which has in pointof fact only a relatively low solubility, is suflicientlysoluble to beused; other examples of suitable salts are calcium chloride and calciumbicarbonate. It might be added that so calcium carbonate itself is forpractical purposes insoluble in water.

It is of advantage, especially when adding saponified tall oil asflotation agent, to use a pulp from which the bulk of the particlesbelow 10 microns in size have been removed, for example by centrifuging.Furthermore, it is also ofadvantage to add the saponified tall 611 orother flotation agents (orthe greater part thereof) to the pulp whilethe latter is'in a concen- 40 trated or dense condition (it maybe justfluid) and to dilute the pulp before flotation, the mineral acid ormetal salt being then added during or after the dilution. Thus themineral acid or metal salt can conveniently be dissolved in the dilutionwater.

In some cases, where an alkaline earth metal. 1

salt is being used, it may be possible to incorporate sufiicient of thesalt in the pulp by forming the pulp from a natural hard watercontaining for instance calcium bicarbonate or sulphate, or part of thenecessary metal salt may be introduced in this way.

The water obtained when dewatering the concentrate from the flotationand also that ob tained from dewatering the slimes (where these areseparated out before flotation) can be used again in the grinding orelsewhere in the process, in which case the process can be carried outin such a way that the make-up water required, which normally isintroduced in the mills, classifiers or thickeners, is instead all addedas dilution water before the flotation step. The supply of mineral acidor metal salt required to support the process can then be introduced inthis makeup water.

The process of the invention is especially 'useful in treatingrelatively coarse pulps of coarsegrained ores.

The mineral acid or metal salt need not be added before the flotation(although this is us ual) but may be added during flotation, or it maybe added in stages. Thus part may be added before flotation and partduring flotation, or portions may be added at different stages duringthe flotation. The acid or salt may be introduced between twoconsecutive flotation cells. The modifying agent may thus be added atany of a number of pointsprior to the completion of flotation.

Example A series of tests was made with a slurry of a ground low-gradelimestone containing 43.8%

0800: in c Co in Modifying agent cleaned con- 8 centrate P PercentPercent None 71.0 4.6 CaOh 84.8 12.2 08(HC03) 84.3 1.5 880 80. 8 18.H1504 84.5 9.3

I claim:

1. In theseparation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by subjecting the pulp to froth flotation in thepresence of a collecting agent capable of floating the calcium carbonateand a resinate frothing agent, and prior to the completion of flotationdecreasing the concentration of resinate dissolved in the pulp byincorporating in the pulp an' inorganic compound capable of forming aresinate .of low solubility selected from the'class consisting ofmineralacids and alkaline earth metal salts which have a solubility-inexcess of that of the corresponding resinate salt.

2. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by removing from the pulp the bulk of the particlesoriginally in the pulp below 10 microns in size, and thereaftersubjecting the pulp to froth flotation in the presence of a collectingagent capable of floating the calcium carbonate and a resinate frothingagent, and prior'to the completion of flotation decreasing theconcentration of resinate dissolved in the pulp by incorporating in thepulp an inorganic compound capable of forming a resinate of lowsolubility selected from the class consisting of mineral acids andalkaline earth metal salts which have a solubility in excess of v thatof the corresponding resinate salt.

- 3. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by adding to the pulp while in a concentrated form acollecting agent capable of floating the calcium carbonate and aresinate frothing agent, diluting the pulp, subjecting the diluted pulpto froth flotation, and prior to the completion of flotation decreasingthe concentration of resinate dissolved in the pulp by incorporating inthe pulp an inorganic compound capable of forming a resinate of lowsolubility selected from the class consisting of mineral acids andalkaline earth metal salts which have a solubility in excess of that ofthe corresponding resinate salt.

a. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent toa'pH value of 6 to 9, the process which comprises improving thecleanness of the concentrate by adding to the pulp while in aconcentrated form a collecting agent capable of floating the calciumcarbonate and a resinate frothing agent, diluting the pulp, decreasingthe concentration of resinate dissolved in the diluted pulp byincorporating therein an inorganic compound capable of forminga'resinate of low solubility selected from the class consisting ofmineral acids and alkaline earth metal salts whichhave a solubility inexcess of that of the corresponding resinate salt, and thereaftersubjecting the diluted pulp to froth flotation.

5. In the separation of calcium carbonate particles from a pulpcontaining such particles, the

pulp having an alkalinity equivalent to a pH- ing the pulp, subjectingthe diluted pulp to froth flotation, and prior to the completion offlotation decreasing the concentration of resinate dis-v solved in thepulp by incorporating in the pulp an inorganic compound capable offorming a resinate of low solubility selected from the class consistingof mineral acids and alkalineearth metal salts which have a solubilityin excess of that of the corresponding resinate salt, at least a part ofsaid compound being added to'the pulp while dissolved in the dilutionwater. 6.- In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent toapH value of 6 to 9, the process which comprises im- "proving thecleanness of the concentrate by adding to the pulp while in aconcentrated form a collecting agent capable of floating the calciumcarbonate and a: resinate frothing agent, diluting the pulp with anatural hard water, subjecting the diluted pulp to froth flotation, andprior v dissolved in the said natural hardwater.

'7. In the separation of calcium carbonate particles from a 'pulpcontaining such-particles, the

pulp having an alkalinity equivalent to a pH value of 6 to 9, theprocess which comprises improving the cleanness of the concentrate bysubjecting the pulp to froth flotation in the presence of a collectingagent capable of floating the calcium carbonate and a resinate frothingagent, and prior to the completion of flotation decreas-f ing theconcentration of resinate dissolved in the pulp by incorporating in thepulp an inorganic acid thereby to form a resin acid of low solubility.

8. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by subjecting the pulp to froth flotation in thepresence of a collecting agent capable of floating the calcium carbonateand a resinate frothing agent, and prior to the completion of flotationdecreasing the concentration of resinate dissolved in the pulp byincorporating in the pulp a minor proportion of sulphuric acid.

9. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the clearmessof. the concentrate by subjecting the pulp to froth flotation in thepresence of a collecting agent capable of floating the calcium carbonateand a resinate frothing agent, and prior to the completion of flotationdecrease ing the concentration of resinate dissolved in having asolubility less than that of the alkaline earth metal salt.

10. In the separation of calcium carbonate particles from a pulpcontaining such particles, the

pulp having an alkalinity equivalent to a pH value of 6 to 9, theprocess which comprises improving the cleanness of theconcentrate bysubjecting the pulp to froth flotation in the presence of a collectingagent capable of floating thecalcium carbonate and a resinate frothingagent, and prior to the completion of flotation decreasing theconcentration of resinate dissolved in the pulp by incorporating in thepulp a minor proportion'of a calcium salt capable of forming a resinatehaving a solubility less than that of the calcium salt.

11. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by sub and prior to .the completion of flotationdecreas-- ing the concentration of resinate dissolved in the pulp byincorporating in the pulp a minor proportion of calcium chloride. I

12. In the separation of calcium carbonate par-.

ticles from a pulp'containing such particles, the

pulp having an alkalinity equivalent to a pH value of 6 to 9, theprocess which comprises improving the cleanness of the concentrate bysubjecting the pulp to froth flotation in the presence of a collectingagent capable of floating the calcium carbonate and a resinate frothingagent,

and prior to the completion of flotation decreasing the concentration ofresinate dissolved in the pulp by incorporating in the pulp a minorproportion of calcium bicarbonate.

13. In the separation of calcium carbonate particles from a pulpcontaining such particles, the pulp having an alkalinity equivalent to apH value of 6 to 9, the process which comprises improving the cleannessof the concentrate by subjecting the pulp to froth flotation in thepresence

